The present invention relates to a cable connection device for attaching an end of a cable to a tool, such as an instrument for use in an oil and/or gas well, which device comprises a housing and a clamping device for securing the cable, which clamping device is attached to the housing and comprises a first clamping body enclosing the cable and a second clamping body attached to the housing.
Several methods exist for attaching a cable or a wire to an end piece. A common method is to shrink the cable on, but this has the disadvantage that it produces unacceptable shear forces in the cable, which may result in short-circuiting of the wires inside the cable. This method is therefore used mostly for wires. Another method is to employ compression sleeve round the cable and a nut, which is screwed over the compression sleeve, thus causing the compression sleeve to clamp round the cable, securing it by means of friction. This provides better control over the clamping forces acting on the cable, since the clamping force is related to the extent to which the nut is tightened. However, this also has the drawback that substantial point forces can be created, which are so great that the cable is destroyed and breaks, or the wires in the cable short-circuit.
It is therefore desirable to provide a clamp connection that provides the least possible clamping force against the cable during normal use, but which offers the opportunity of increasing the clamping force in special cases, up to but not exceeding the cable""s breaking strength.
In the present invention a clamping effect is achieved which acts on the cable over a greater area and which is least where the cable enters the connection. In addition the object is achieved that the clamping effect is increased the higher the tension is in the cable.
This is achieved by the second clamping body having an internal sloping surface, and the first clamping body having an external sloping surface, where the said surfaces interact in order to clamp round the cable and hold it securely.
The connection device according to the invention is particularly suitable for use during intervention in oil or gas wells where a tool or a measuring instrument, which is suspended in a cable or wire, has to be lowered into the well. The cable is employed as a suspension means, i.e. the instrument is lowered or pulled up again by means of the cable. The connection therefore has to be strong enough to hold the tool. Since the cable may creep, it is important that the clamping forces are not greater than is necessary in order to hold the cable. However, the tool or the instruments sometimes become stuck in the well, in which case it is desirable to increase the tension in the cable to its breaking strength without the connection working loose. The connection device according to the invention provides a very good distribution of the clamping force over the connection, which also increases with increasing pulling force.